Year-round growing in a closed system

Fancy goldfish provide nutrients for the nutrient film technique system at Aquaponics Unlimited. The system contributes about 5 percent to total annual production.
Photos by Kathleen Hatt unless otherwise noted.

Growing plants in water recirculated from fish tanks may not be for everyone, but for Mike and Tracy Griffin in New Boston, N.H., it’s the only way to farm. Quick to acknowledge that his growing method is not for the plumbing-impaired, Mike Griffin points to the system’s advantages: “No weeding, no watering!” By combining aquaculture with hydroponics-tilapia with vegetables-the Griffins are able to grow enough produce to feed themselves, sell at farmers’ markets and supply several restaurants.

Growing powered by goldfish and tilapia

Using aquaponics is a new venture for the couple. It all began in 2008, with their goldfish pond and a downturn in Griffin’s construction business. Griffin decided to try a method the Mayans used: growing vegetables on straw rafts in fishponds.

Instead of rafts, Griffin built a structure with PVC pipes to both support the plants and circulate the water. He cut holes, each the diameter of a red Solo cup, into the horizontal pipes at 12-inch intervals. With a soldering iron, he made 20 holes in the sides and bottom of each cup. Water is pumped to the top of the system and circulates through the pipes and cups before traveling back into the pond via gravity.

In its first season, the system produced so much that the Griffins were giving vegetables, greens and herbs to anyone who would take them. The success of this system, known as the nutrient film technique (NFT), led to Griffin’s proposal that they grow food indoors on a larger scale and to the beginning of Aquaponics Unlimited ( The NFT system, used in the summer, contributes about 5 percent of total production.

Deep water culture system

To expand their aquaponic growing to a year-round operation, Griffin added a 22-by-33-foot greenhouse onto an existing 22-by-33-foot barn. Constructed of Douglas fir and other materials certified for organic growing, the greenhouse holds 10 troughs, each 4 feet wide and 24 feet long. With 10 inches of water inside, the troughs weigh 2.5 tons each.

Seeds, mostly from Johnny’s Selected Seeds, germinate in net pots on this two-level seeding table.

This closed-loop deep water culture (DWC) system contains about 90 percent of Aquaponics Unlimited’s plants. Some 3,000 plants cover and are supported by 900 square feet of rafts floating on 10 inches of water. The water flows from two 650-gallon fish tanks through a swirl filter, which removes heavy solids. Finer solids are captured by a screen filter and settling tank. From the settling tank, the nutrient-rich water flows into the raft system, where it bathes the plants’ hanging roots. Plants act to clean the water before it is returned to the fish tanks.

This system supports the growth of many types of lettuce, chard, kale, arugula, watercress, mixed greens, bok choy, escarole, mustard greens, celery, peas, basil, chives, dill, cilantro, parsley and more. The water circulates completely approximately every three hours.

Multiple levers can be used to regulate and control water in Aquaponics Unlimited’s growing system.

A third growing system

A small flood and drain (or ebb and flow) system is also in place at Aquaponics Unlimited. A 12-inch-deep media bed is used to grow carrots, beets, turnips, parsnips, onions and other root crops. Water cycles in and out of the media bed; it is repeatedly flooded and drained. This system accounts for about 5 percent of production.

In all aquaponics systems, aquatic animals and cultivated plants form a symbiotic relationship. In typical aquaculture systems, excretions from aquatic animals can accumulate in the water, increasing toxicity. In an aquaponic system, water from an aquaculture system is fed to a hydroponic (plant-growing) system, where the fish byproducts are broken down into nitrates by nitrogen-fixing bacteria. The nitrates feed the plants.

Marigolds are scattered among plants, such as celery, to control thrips.

Tilapia: Producer and product

When tilapia first arrive at Aquaponics Unlimited, they are tiny – smaller than the smallest joint of your little finger – and not yet producing the volume of nutrients necessary to support growing plants. To start the DWC system, 4 to 8-inch-long fancy goldfish were borrowed from the outdoor pond. As the tilapia grew, the fancy goldfish were returned to the outdoor pond. Tilapia are fed Purina AquaMax and a commercial catfish food supplemented with vegetable greens. Tilapia also eat the algae in the tanks.

Plants, including the celery shown here, grow in red Solo cups.

Tilapia grow to marketable size (1.5 to 2 pounds) in nine to 10 months. At about five-month intervals, new fingerlings arrive to replace fish that have gone to market. Griffin plans to establish his own breeder colony. Males are preferred because they grow faster than females, so tilapia are sometimes hormone-manipulated to produce only males. Breeding Oreochromis hornorum with Oreochromis mossambicus results in hybrid offspring that are naturally 90 percent male, so hormone manipulation is not necessary. The hybrid also contains more flesh per pound than other tilapia varieties. Tilapia is an efficient fish. It is said to have one of the lowest conversion (food-to-fish) ratios of any meat: 1.5 pounds of fish food becomes 1 pound of flesh on each fish.

Tilapia tanks and the associated growing system need 7,000 gallons of water to operate. The water, which comes from the Griffins’ well, is much cooler than the water of tilapia’s native African lakes (80 to 82 degrees Fahrenheit), so it must be heated. Tilapia can live at a slightly lower temperature, especially as they get bigger, but vegetables and herbs don’t like water that’s too warm. As a compromise, water is heated to 75 to 76 degrees Fahrenheit. Air temperature is maintained at a minimum of 60 degrees Fahrenheit by an anthracite stoker furnace.

Plants grow in troughs on two levels of the greenhouse at Aquaponics Unlimited. Mike Griffin uses a repurposed bunk bed ladder to access a hinged plank on which he stands to check plants on the upper level.

The daily routine

“Once built, aquaponics is a lot easier than conventional growing,” says Griffin. “There is no watering and no weeding. It is easier for plants to grow roots, and they grow faster in a good, easily accessible supply of nutrients.” To keep the aquaponics system running, the couple follows daily and weekly routines.


  • Check water level in fish tanks. Add water once every two to three days to replace water that has evaporated or been used by plants.
  • Feed fish two to three times a day. In the future, automatic feeders will be installed.
  • Test water. Fish like a pH level around 7; plants prefer 6.5. Griffin aims for a 6.5 to 6.8 compromise. When indicated, calcium, potassium or iron is added.
  • Check water temperature.

Tracy Griffin transplants net pots of cilantro from the seeding table to a raft that will support the plants while floating in a trough of nutrient-rich water in the greenhouse.


  • Start seeds in net pots. Place two seeds in a mixture of coco coir and vermiculite.
  • Place newly seeded net pots under lights on sprouting table, where they remain until seedlings are about 2 inches tall and roots are visible outside the net pot.
  • Clip extra seedlings if more than one has germinated in each net pot.
  • Take and transplant cuttings.
  • Place sprouted plants with well-established roots into 2-inch-deep blue foam rafts.
  • Harvest produce for market.
  • Catch largest fish for market.
  • Check the generator. Uninterrupted electricity is essential to power the blower used to oxygenate the fish tanks. If the blower goes off for an extended period of time, the fish could die and plants might be susceptible to root rot.

Mike Griffin is building this mini ebb and flow system for home gardeners to use outdoors in summer and indoors in winter.

To market, to market

Aquaponics Unlimited is relatively new to the retail market. The Griffins participate in the Milford Farmers’ Market from June through October and two winter farmers’ markets, the Milford Farmers’ Market and the Bedford Fields Market, held alternating Saturdays. About 30 tilapia are brought to each market. Since Aquaponics Unlimited’s facility is not USDA-licensed, the fish are sold whole, with a 1.5 to 2-pound fish selling for $8. Future plans include filleting fish in a rented, USDA-approved space.

Tilapia grow in two 650-gallon tanks sold as watering troughs for cattle. When they reach about 2 pounds, the fish are caught and sold.

To help increase sales at the farmers’ markets, Tracy prints recipes that feature their products. “I’ve noticed that people pick up several recipes, buy our products, then go around the market collecting whatever ingredients we don’t offer that week,” she says. Along with the recipes, they also provide instructions for cleaning and preparing fish.

Tilapia are fed Purina AquaMax and discarded greens. They also eat algae from the tanks.

A growing business

In conjunction with the tilapia market, Aquaponics Unlimited is looking to specialize in a few crops, some of which will grow in a 30-by-80-foot greenhouse to be built next season through a $7,500 Natural Resources Conservation Service grant. Although it will initially be a stand-alone structure, the greenhouse may be integrated with the original system in the future. They also plan to market a compact flood and drain system built by Griffin and designed to operate on a deck in the summer and indoors for the winter months.

Kathleen Hatt is a freelance writer and has been a frequent contributor to Growing since 1998. She resides in Henniker, N.H.